Optical fiber technology is well suited for communications applications because optical fibers have a wide transmission bandwidth and relatively low attenuation. However, optical fiber interfaces to electronic and optical networks are expensive to manufacture because of the difficulty associated with mounting laser transmitting and receiving devices onto substrates and aligning them with separately mounted optical fibers. The difficulties generally are associated with manufacturing components with precise tolerances and mounting components at precise locations within precise tolerances. The challenges of alignment are typically faced during the packaging of the devices. To overcome these difficulties, the transmitter and receiver devices can be enlarged so as to alleviate the tight tolerances that are difficult to achieve during alignment.
In a conventional optical fiber communications system, a transmitter sends optical data into a fiber, and the data is received by a detector at the receiving end. Two inherent interfaces exist at both ends of the fiber. Minimizing the optical loss at these two interfaces is difficult due to the alignment at the micron scale. Alleviating the alignment tolerance at the transmission end can be done by enlarging the core of the optical fiber. However, this has an undesirable effect at the receiving end interface. Namely, the light that exits a larger core fiber has a larger cross-sectional area, thereby making it difficult to capture the light.
Large core fibers, e.g. fibers with core diameters of 50 to 63 microns, are typically found in local area network (LAN) environments. The large cores provide more tolerances for installation than smaller core fibers, e.g. coupling the fiber to a source laser or a receiving photodetector, as well as coupling fibers together with an optical connector. Two types of photodetectors are typically used to receive the light from the fiber and convert the light into an electrical signal, namely a PN diode and a metal semiconductor metal (MSM) diode. Both are currently made to be about 70 to 80 microns in diameter, so as to capture the light from the LAN fibers.
Another type of fiber is being used in limited applications, namely the hard clad silica fiber (HCS) fiber. This fiber has a silicon core surrounded by a hard plastic cladding and has diameters of typically 200-300 microns.
A further type of fiber is a plastic fiber. This fiber is similar to the HCS fiber, but uses a plastic core instead of a silica core. Since the core is plastic, the attenuation of the fiber limits effective use of the fiber to distances of 10 meters or less.
Accordingly, there is a need for an optical receiving assembly that incorporates all the necessary optical and electrical components to capture the light exiting the large area fiber of a low cost platform.